1. Field of the Invention
This invention relates to a process for producing articles having a desired shape, e.g. tubes, rods, plates, crucibles, gaskets, etc., from acetylenic polymers and, where desired, thermolyzing such shaped objects to produce carbon objects having the same shape. More particularly, this invention relates to a process which involves preparing a hot solution of the polyacetylene in nitrobenzene or a halobenzene solvent having a boiling point greater than 100.degree.C., allowing the hot solution to cool in contact with at least one shaping surface, for example, a mold, a casting surface, etc., to a temperature where the solution solidifies to produce either the desired final shape or to produce an intermediate shape which is then converted to a final shape, for example, by cutting, carving, heat forming, boring etc., and thereafter removing the solvent from the solidified final shape. On heating these shaped articles to an elevated temperature the acetylenic polymer decomposes to carbon without changing shape and little, if any, change in size. Once carbonized, the articles can be converted to either vitreous carbon or graphite articles without change in shape and little, if any, change in size, by heating using known vitrifying or graphitizing conditions.
2. Description of the Prior Art
Polyacetylenes are relatively new polymers having many interesting and desirable properties. They were first described by Allen S. Hay in J. Org. Chem. 25, 1275 (1960) and 27, 2320 (1962). Subsequently, a much broader class of polyacetylenes was disclosed and claimed in Hay's U.S. Pat. Nos. 3,300,456, 3,332,916 and 3,594,175. Using Hay's process of oxidatively coupling compounds having two acetylenic groups, Sladkov et al. likewise prepared polyacetylenes which they describe in Bull. Acad. Sci. U.S.S.R. -- Div. Chem. Sci., English Translation [7] 1220 (1963). All these polymers and copolymers described in this prior art have, as a common property, a butadiynylene group, i.e., --C.tbd.C--C.tbd.C--, dispersed along the polymer backbone. They also have in common the fact that they are formed by oxidative coupling of organic compounds having two ethynyl groups, i.e., --C.tbd.CH. In the oxidative coupling reaction, thoroughly described by Hay in his above patents and publications, the hydrogen is removed from the ethynyl groups by the oxidation reaction to form water and one of the resulting ethynylene groups of one molecule is joined to one of the resulting ethynylene groups of another molecule to form the butadiynylene groups of the polymer molecule. It is these latter groups which cause the polymers to be very thermally unstable and photosensitive and which tend to make the polymer difficulty soluble in common solvents for polymers.
It is obvious that these polyacetylenes are entirely different in kind than polymers containing isolated ethynylene groups in the polymer molecule. Typical of such polymers are the polyesters obtained by esterification of an acetylenic dicarboxylic acid and a glycol or esterification of a polycarboxylic acid with an alkynediol and polyethers obtained by the reaction of acetylenic glycols with dialkyl acetals or with alkylhalohydrins. These polymers have ethynylene, but not butadiynylene groups, along the polymer backbone. Such polymers are not included in the term polyacetylenes.
Because of their thermal instability, it is impossible to mold articles from the polyacetylenes using heat and pressure. Those polyacetylenes which are at least soluble in hot solvents can be cast into films by well known solution-casting techniques, spun into fibers by spinning a solution of the polymer by well-known solution-spinning techniques or by extruding the powdered polymer which has been blended with a sufficient amount of a plasticizing solvent so that the polymer can be extruded at a temperature below its thermal decomposition temperature. Any of these shaped articles can be thermally decomposed to convert them into a carbon film or fiber which can be graphitized. It would be highly desirable to be able to form the acetylenic polymers into articles having their shapes which also could be converted to carbon articles of the same shape, especially those having substantial mass or cross-section.